External wireless devices are often used to monitor ECG in humans and animals for clinical care and in research studies. For example, ambulatory devices that measure electrocardiogram are routinely used to assess arrhythmias in human clinical studies and for diagnosis of the status of patients that may be at risk of arrhythmias. Correlation of symptom and rhythm is often a goal of such evaluations, but limitations of current devices often preclude the ability to do so. Ambulatory monitoring devices often include a button that the patient or a care provider presses when symptoms occur. Pressing the button then results in an event mark in the recording. Patients or care providers are advised to keep a diary that describes the nature of the symptoms. Some devices may include a computer aided function intended to simplify recording of the nature of the symptoms. For example, some devices have a menu displayed on a touch screen that allows the patient to select a description of the symptoms from among a list. Whether a diary or a computer-aided tool is used, a low percentage of patients provide a record of the symptoms associated with an event mark. This limits the ability to correlate symptoms and rhythm and hence reduces the potential diagnostic utility of the system.
Another limitation of current devices is that they must be removed prior to bathing or showering in order to avoid damage from fluid ingress. The devices can be damaged due to exposure to fluid for any reason including falling in the water, exposure to heavy rain, or accidentally leaving a device in a pocket of a garment during washing. This limitation not only creates an inconvenience for the patient but also can result in damage to the device and subsequent expense for the patient, care provider, supplier, or insurer.
Yet another limitation of current device is that measurement of long-vector ECGs (i.e. where at least one electrode is located separate from the electronics housing at a distance of at least 10 cm) often requires the use of a relatively expensive connector and cable harness that can constitute a significant portion of the cost of an ambulatory device.